1. Field of the Invention
The invention relates to a printed paper identification system, and more particularly, to a printed paper identification system for identifying whether a printed paper is a falsified document.
2. Description of the Prior Art
Vending machines are widely used for selling various consumer products in the present market. Since some vending machines accept paper money, it is important for a vending machine to determine whether a paper money is a falsified one. Please refer to FIGS. 1 to 3. FIG. 1 is a schematic diagram of a prior art printed paper identification system 10. FIG. 2 is a top view of a printed paper 16. Areas with different brightness are shown in different textures to indicate their different gray levels. FIG. 3 is a detected signal 24 generated by the printed paper 16 shown in FIG. 2.
The printed paper identification system 10 comprises a paper passage slot 11, a propeller 18 for driving the printed paper 16 through the passage slot 11, an LED (light emitting diode) light source 12 and a correspondent light sensor 14 installed separately at two opposite sides of the passage slot 11, and a controller (not shown) electrically connected to the propeller 18 and the light sensor 14 for controlling the propeller 18 to drive the printed paper 16 through the passage slot 11 so that the light sensor 14 can detect the light emitted from the light source 12 and transmitted through a strip area 22 of the printed paper 16, generate a correspondent detected signal 24 as shown in FIG. 3, and compare the detected signal 24 with a pre-stored identification signal to determine whether the printed paper 16 is a falsified document. The identification signal is usually generated by feeding a real printed paper into the system 10 and storing the detected signal generated by the real printed paper in the memory of the controller as the identification signal.
The printed paper 16 can usually be correctly identified by comparing its detected signal 24 with the identification signal stored in the system 10. However, printed papers such as paper money are frequently held by hand or clamped in wallets, the quality of the printed paper 16 may greatly affect its detected signal 24. For example, the color or pictures printed on the surfaces of the printed paper 16 may fade away after long use. Such fading can usually cause a great variation over the waveform of the detected signal 24, and make it very difficult to be identified. The system 10 usually allows certain degree of tolerance over the detected signal 24 generated by the printed paper 16 so as to allow a real printed paper 16 to pass the test. A small tolerance can allow the real and perfect printed papers to pass through the test, but may fail used real printed papers. However, a big tolerance may allow both the used printed papers and falsified printed papers to pass through the test and such condition is not acceptable.